


Oh The Fire Is So Delightful

by TheNinjaMouse



Category: Undertale (Video Game)
Genre: Another Christmas special for the OoF universe, Established Relationship, F/M, Gen, This is not canon to the main story, but if you haven't what are you even doing??, ninja's first lemon, nor it is required that you read OoF before this
Language: English
Status: Completed
Published: 2019-01-03
Updated: 2019-01-03
Packaged: 2019-10-01 01:03:30
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,627
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17234489
Author URL: https://archiveofourown.org/users/TheNinjaMouse/pseuds/TheNinjaMouse
Summary: It's Christmas time once again and you've got a special surprise for Grillby





	Oh The Fire Is So Delightful

**Author's Note:**

> Merry Late Christmas! You all voted, so here it is! Be kind, this is the first time I've ever written anything like this, so I hope you like it! Have a happy new year and I look forward to making even more stories in 2019!

You’re not really a follower of trends. Sure, if it’s something you take interest in, you’ll indulge occasionally but most of the time, you tend to lose interest when something starts getting popular. Your long-ago discard fidget spinner and forgotten jar of stress slime are a testament to that. But once in a while, a trend rises that brings back something from your childhood. A treasured nostalgia kind of thing. Something so dumb and childish that you can’t help but to dive headfirst into it.

Onesies. Union suits. Kigurumi. Whatever you wanted to call them, the pajama suits from your childhood have made a comeback and it was with no small amount of glee you visited various websites to find the perfect one for you. And while you were searching, you came across one that would look absolutely adorable on a certain someone else. So you added it to your cart as well and ever since the two arrived, you’ve kept quiet about it until Christmas Eve. There’s going to be a big get together with everyone Christmas day, with all of the food, gifts and noise to go with it. So you and Grillby decided to have a quiet night in for the 24th, perhaps watch a movie and make some hot chocolate. You’ve packed your bag for the night, including your new onesie. 

So now you just have to figure out how you’re going to convince him to wear his.

His entire place smells of cinnamon, holly and of course, camp fire smoke. The bar has been decked out in subtle but cheerful Christmas decorations. Garlands tipped with red and gold ornaments, twinkling golden lights hanging down from the ceiling and a tree adorned with hand made decorations made by customers give the room a bright flair. While Grillby himself was content to mostly keep the decorating in the bar, you’d pulled him into making the upstairs festive as well. There are a few garlands, fairy lights hung up near the ceilings, the now traditional surfing Santa on the fireplace mantle and a smaller tree up here with soft gold and blue lights and various ocean and cooking themed ornaments.

And a cut out of Chris Pine at the very top.

You adjust the surfing Santa slightly, enjoying the heat from the fireplace. Grillby had it recently installed, and you’ve taken full advantage of it when you come over to visit. Boyfriend made of fire notwithstanding, there’s something unbelievably cozy and relaxing about having a crackling fireplace. It’s gently popping now, glowing with light as you finish turning on a selection of jazzy Christmas music while Grillby pulls some mugs down from the cabinets. He’s got everything prepared for hot chocolate on the countertop and the kettle of hot water is just starting to steam quietly.

Okay, it’s now or never. You grab the two flat boxes you’d slipped under the tree earlier and cross into the kitchen. Grillby looks up, his gentle smile turning to curiosity. He tilts his head.

“Okay, so, I got us something! It’s a thing from my childhood, I thought it would be a lot of fun.” It’s hard to hide your growing grin but you keep your voice as casual as you can. You hold one of the boxes out to him, setting yours down on the counter. “Here, go ahead and open it.”

He takes the box from you, narrowing his eyes slightly at your growing gleeful expression. But still he opens it. And goes still once he sees what’s inside. “What is this exactly?”

“Pull it out and see!”

Slowly, he gathers up the fabric in one hand and pulls it out, setting the box aside. The onesie unfolds, revealing an absolutely adorable dark teddy bear design. Grillby stares at the smiling face on the hood before slowly looking back at you. “I still don’t know what this is.”

“It’s a onesie!” You pull your box over and pull yours out, revealing the gray kitty cat onesie you picked for yourself. It was a true fight to decide between this one and the shark one, but in the end, the cat looked comfier. “They’re pajamas from when I was a kid!”

“You’re supposed to…wear these.”  

“Yeah!” You hold yours up against your body. “Isn’t it cute?”

He’s quiet for a long moment before far too lightly saying, “On you, yes, it is,” as he moves to put the bear onesie back in the box.

You grab his wrist. Staring up at him with wide doe eyes, you whisper, “Don’t you like it?”

He flickers nervously. “…. It’s just-”

“Just what?”

“…Not my style?” he offers weakly.

“You wear pajamas, don’t you?” You gently take the bear out of his hands and hold it up against him. “These are just another kind of pajamas. And it’s Christmas! You wouldn’t refuse my Christmas wish, right? Just for a bit.”

“I’d rather not.”

“Please?”

 “I don’t think so.”

You narrow your eyes. That’s how it is huh? Time for the Ultimate Sad Puppy Dog Face. You bat your eyelashes, let your mouth curve into a hopeful pout and let your lip just barely quiver. In your eyes is the shine of unshed tears that threaten to fall should he refuse you again.

He looks away. “Stop that, that’s cheating.”

You shift to meet his gaze. When he stubbornly looks away again, you lift yourself up on your tippy toes, leaning close to the side of his head. “And…if you wear it for even a little while, I’ll give you something even better later.”

He sucks in a quiet breath. He looks back to you, meeting your gaze. You waggle your eyebrows, grinning.

He sighs deeply before taking the onesie from you. “You’re the worst.”

“Thank you!” You sing song after him as he vanishes into his room. You allow yourself a little fist pump. _Success_! You snatch your own and duck into the bathroom. You need to change and be ready, so you can see the full glory of Grillby in a bear onesie the moment he comes out.

You shed your clothes and slip into the soft, plush fabric. A quick zip and a moment of checking in the mirror (hot dang, you’re cute!) and you’re good to go. You hurry back out to the empty living room and kitchen. His door is still closed. You give him a few minutes before going over and knocking on the door. “Grillby, come on now, it doesn’t take that long.”

His voice, muffled and sullen, floats through the door. “I look ridiculous.”

“It’s just me, there’s no reason to be embarrassed! Besides, I look ridiculous too. That’s what makes it fun!”

There’s a moment more of silence and then the knob starts to turn. You step back, your heart eagerly racing. The glow of his blush is visible before he is and you throw your hands up over your mouth in a desperate attempt to stop your laughter before it can burst out of you.

 _He’s adorable!_ He literally looks like a giant teddy bear, save for his entirely blue head, which is smoking little white puff clouds as he stares down at his bare feet. When he finally looks up at you, you lose it. You move past laughing and explode into uncontrollable howling, nearly falling over from the force of it. Tears prick at your eyes as Grillby steams even more. Not a trace of orange or gold remains, completely overtaken by blushing blue. He whirls on his feet.

“I’m changing.”

“No!” Lurching forward, you manage to snag him before he closes the door and wrap your arms around his waist. He starts, twisting his head back to look at you and you lose it again. A few tears actually manage to escape. “N-no, I’m sorry, you’re-” You actually can’t even speak, and you bury your head in his back, reduced to wheezing. “You look f-fine, perfectly fine, I’m sorry, I can’t s-s-stop-!”

A shrill whistling interrupts you and you jerk your head up to see the kettle absolutely spewing steam. Grillby twists in your loosened grip. “Would you mind grabbing that? _Thank you._ ” And he escapes from your grasp, shutting the door behind him. That sneak! You dash over to the stove, barely remembering to grab an oven mitt before easing the kettle off of the burner and turning the burner off. And then you run back to his bedroom door, flinging the glove aside. If he’s gonna play dirty like that, he’s going to have to face your pure wrath!

You twist the handle and-yes! He didn’t lock it! You shove the door open, standing there in your kitty kigurumi glory. Grillby, in the process of unbuttoning his onesie, barely has a chance to yelp before you run and jump straight at him. You slam into him, wrapping your arms and legs around his body. He staggers and flails, knocking into the bed and topples back, pinned by you. You sit up, keeping him trapped with your knees and waggle your finger in his face.

“Sir! You can last more than thirty seconds in a onesie! It’s not going to kill you!”

He’s gaping up at you, still utterly flushed blue. “Are you crazy?” he finally wheezes.

“This is our second Christmas together, I thought you'd already answered that yourself." You gently boop his nose…area and reach for his open buttons, pulling them back together. “Now, give this thing a chance, you might actually like it.”

He glances down at your hands gently fixing his onesie. After a moment, he flickers with a smirk. “Wouldn’t you normally want the clothes off in a situation like this?”

You choke, eyes darting to his. He takes advantage of your frozen, blushing state to put his hands on your shoulders and roll over. Now he’s above you, knees between yours. You hadn’t quite finished buttoning his clothes so one shoulder is partially bared. Your heart leaps into your throat.

He leans down close, golden eyes lidded sweetly. “Well? Wouldn’t you say so?”

You swallow instinctively, unable to stop your gaze from flicking to his mouth. He must see the want in your eyes because he leans down and presses a deep kiss against your lips. You sigh into it, your hands rising to take hold of the soft fabric of his bear onesie, pulling him closer to you.

Wait a minute.

You break away with a gasp. “Oh, you’re good,” you scold, narrowing your eyes as he pulls away slightly with an all too innocent tilt to his head. “But you’re not getting out of this so easily.”

“Aren’t I?” Smug jerk, he’s too pleased with himself. He touches the top of your zipper lightly and a deep thrill makes your body shiver.

“No, no stop that.” You gently smack his hand away. “You’ve got to give me at least an hour in the onesie. At _least_. Or-!” Struck by a sudden idea, you grin widely. “Why don’t we play a game? Winner decides if the onesie stays on or not.”

He’s considering it. “What game?”

You bite your lip. “Chess,” you finally decide. Okay, yes you haven’t beaten him yet but there’s always a first time, right? And even if you do lose, if you draw the match out, you’ll get to at least see him in the onesie for a while.

A soft pop sounds from his flames. “....Fine. But." He leans down close again, letting his heat wash over your face. "I won't go easy on you." 

You can't take it any more. You break into giggles. He makes a face at you, pulling away. You wave your hand. "Sorry, I can't take you seriously dressed like this. It's quite _unbearable_."

He groans loudly. His color had started to go back to normal but he blushes again in the face of your laughter. "And who's fault is that?" he grumbles. He shifts and finishes buttoning the outfit as you sit up too. You scoot over and kiss his cheek. He just huffs quietly at you. But if you're not mistaken, as you hop off the bed and sashay into the living room to grab the chess set, you can feel his gaze lingering on your backside. You make sure to wiggle your hips a little more than necessarily needed. There's a thick blanket on the back of the couch that you grab and spread out on the floor in front of the fireplace. As you pull out the chess set and set up the board, Grillby takes care of the hot chocolate. Your gaze keeps darting to him and the sight of him in the teddy bear outfit is almost enough to send you into another fit of giggles. You do lose the battle when he turns his back to you and you catch sight of the tiny tail on his butt. You snort so loudly it actually hurts and roll over on the blanket when he shoots you a dark glare.

Once you recover from the fit, he brings over two mugs of steaming hot chocolate. Yours is topped with a generous mountain of whipped creamed, sprinkles and a peppermint stick. His is a little more simple, with just the peppermint stick and a few marshmallows. You slip the sleeves of your onesie up over your hands before taking the mug. Even through the fabric, you can feel the warmth seeping into your hands. You blow gently on it a few times before nibbling at the whipped cream. Grillby sits cross legged and sips at his drink without bothering to check the heat. You'd long ago learned that unless it was pure water, he could in fact drink liquids. He just usually preferred not to unless it was a special event or a drink made with magic to ease the sting of it on his throat.

He lowers his mug. He's softly staring at you, very slowly taking you in. It's funny how easily he can make your heart race with just a look. Setting his mug to the side, he reaches for you and places his hand on your cheek. Your breath catches. His thumb gently rubs over your cheek and you lean into the touch. He slowly moves his hand down, lightly trailing over your neck. Then he grabs the hood of your onesie, pulls it up and yanks it down over your eyes, making your squawk loudly. "Let's get started so I can get out of this thing." 

You push the hood back just enough to see, sticking your tongue out at him. "Please, I'm gonna win this time, for there is far more at stake than my pride!" 

He hums noncommittally, nodding at the set. "You first then." 

Grinning, you set your mug down and crack your knuckles, making him wince. For a while, you just play, content to sit in silence with just the music in the background. Silence has always been comfortable with Grillby. It's one of the things you love about him. You take your time with each move, carefully thinking ahead and trying to guess what moves he might try to pull on you. He's one of the best tacticians you've ever met and not just at chess. When he normally plays, he'll barely need a moment to see what the best move is and how events will play out. Trying to beat him at planning has never worked but what has gotten you close is being spontaneous. Keep him guessing, take advantage of openings as they pop up. You've come close to beating him that way, until he was left with just his king, a rook and a pawn. And yet he still managed to put you in checkmate right before you could corner him. 

Before too long, your cocoa is gone and you're starting to sweat and not just from the intensity of your concentration. Your belly full of hot chocolate, a roaring fire beside you and a living fire in front of you is really starting to make you feel the heat. The fleece onesie is not helping in the slightest. You shift, moving from a sitting position to laying down on your belly and push the legs of your pajamas up with your feet to try and relieve some of the heat.

Grillby's gaze shifts from the board to you, watching as you find a new, comfortable position. "You're looking a little red there," he points out, taking another slow sip at his drink. 

"Just excited about finally beating you." You push the hood off your head, squinting at the board. Okay, it's down to the last few rounds. You've got this! You move your knight up to a seemingly random spot and then look up at Grillby. He's got his chin in his hand and has a soft hue of color to his flames. You smile back at him and gently say, "It's your turn Sparks." 

He blinks, fire popping and blushes. He looks back down at the board and moves his own knight. "Checkmate." 

"What!?" You sit up. Flabbergasted, you stare at the board and try to see if there's any way out of the checkmate. "No way! How did I not see that?!" 

He's grinning now as he watches you squint, trying to find an escape that isn't there. "You were close. But you don't keep an eye on all the pieces like you should." 

You slump back and roll onto your side, groaning loudly. "And I didn't even draw out the game as long as I should've." Damn it! And now he's gonna take the onesie off. Oh well, at least you got to see him in it at all. You wave your hand grumpily. "Fine, you win, you can take it off." 

You hear him shifting, probably getting up to leave to change. When you peek up, your mouth pops open. He's moved the chess set out of the way and moved a little closer. "I do believe that the deal was the winner decides if the onesie stays on or not," he says softly, teasingly. "But we didn't say which one." 

You lift yourself up to your elbows. "Oh yeah?" you return, letting your own teasing grin lift your mouth. "I suppose we didn't." 

He's even closer now and then he places an arm on either side of you, effectively trapping you in. "And I'm concerned that you might be overheating in this thing." 

"I suppose I am a little warm," you whisper, angling your head back to expose your neck. "But you know I can take the heat." 

He lowers his head, mouthing at the skin under your cheek. You sigh, curling your fingers into the blanket. His own fingers rise to play with the zipper of your onesie. "Better to be safe than sorry," he murmurs. He pulls away and looks you in the eyes, his seductive aura fading for just a moment. "Is this okay?" he asks, as he always does. 

In answer to that, you take his hand and guide him to your heart so he can feel it racing under your skin. "Yes. For you, it will always be yes." And then you catch his mouth with yours, releasing his hand so you can place it on his neck and pull him closer. He returns the kiss with intense enthusiasm so you let your mouth open and your tongue flick out to tease against the harder edges of his mouth. His hand moves to support your back as he shifts so that he's now straddling you. The growing heat in your stomach only flushes deeper with his weight pressing against you. 

With his free hand, he tugs at the zipper of your pajamas, pushing at the edges until your shoulders are bared and he swaps his hands so that he can touch your skin rather than the fabric. You giggle against his mouth. "Come on, admit it. The onesies were a fantastic idea." 

"Shut up and undress me," he growls in a way that sends an excited shiver up your spine. You do as he asks, fully leaning on his hand as you lift your arms up to work at the buttons of his suit. You slip your hands inside and lay them flat over his chest. He shivers, flames crackling noisily. You yelp when he suddenly sits up, pulling you with him. He releases you just long enough to shrug out of the sleeves so that the onesie pools around his waist. You take the opportunity to rearrange yourself so that you're the one sitting on him and let your own onesie fall to your waist as well. 

You both pause for a moment, taking each other in. You, with human skin, scarred, imperfect and soft. Him, living fire and magic combined in a strange and wonderful way that still doesn't completely make sense. This isn't the first time you've been intimate like this but without fail, each time you do this, you can't help but marvel at how unfairly gorgeous and...well, _hot_ he is.

He gently rubs his hand over your face and down your neck, then lower and he breathes, "Stars, you're beautiful." 

Laughing quietly, you press your forehead against his, breathing in the scent of him, all fire and smoke and spice. You pepper kisses all over his face and the heat leaves your lips tingling in a maddening sort of way. His hands return to your back and dip lower, squeezing the soft curves there until a soft moan forces it's way out of your mouth. You can feel his reaction to that, a subtle shiver that makes his flames pop. And when you shift your hips just slightly, pressing even closer against him, that small shiver turns into a a full body quiver while his flames flash with bright golden colors. He presses his face into the crook of your neck.

"I should probably reward you for putting up with my antics." Your voice is a little more breathy than you'd like to admit but it only seems to encourage Grillby to hold you tighter. 

"...What did you...have in mind?" he asks between pressing scorching kisses against your skin.

You reach down and tug at the clothing still between you. "We might want to get rid of these first." 

He snorts against your neck. "Oh _now_ you want to get rid of them." 

"Or we could put them back on, maybe do taxes or whatever instead." 

The speed at which he lifts you up and off his lap so he can pull the pajamas off all the way sends you into another laughing fit. Your laughing turns into a squeal when he pulls yours off the rest of the way as well, throwing them into a heap. His glasses go too and the intensity in his golden eyes steals your breath away before his kisses have a chance to do the same. Flesh to fire, you lose yourself in sensations and pleasure, touching, teasing and panting from the intensity of the heat both inside and out. You're sweating and in the places his flames lick at your skin, steam rises and hisses softly. 

When you break away for air, you lightly press your fingers against his chest and push gently. He follows the motion until he's lying on his back. You move slowly, running your hands up and down your sides and remove your underwear. His breath hitches, lovely blues overtaking his face. He tries to sit up but you stop him, placing your hand back on his chest. There's a fluttering under your touch, his Soul racing at the sight of you above him. You let your hand slowly slide down, trailing over the plane of his stomach, lingering on the scars there and then stop at his hip as you climb over him. The spike of heat that courses through you at the expression on his face nearly makes you lose yourself right then and there and you have to take a moment to breathe deeply. 

He's watching you. "Still okay?" he asks softly. 

He's so considerate, even in the middle of something like this. You rub your thumb over his hip. "I'm more than okay," you assure him. Then you grin devilishly. "Are you?" You press against the most intimate part of him, lightly, teasingly. A tremor shakes him as he moans and his head flops back. His hand shoots up to grip at your thigh. 

"Stars Shore," he gasps, sucking in quick breaths of air. 

"Hmm?" 

"... _Please_." 

You twist your finger through the flames on his chest. They cling to your skin, little whispers of heat. "Tell me what you want."  

His flames are shifting with a myriad of colors, painting your skin with light. His chest is heaving, glowing with the strength of his Soul beating below the flames and his _eyes_. Oh, his beautiful, golden eyes are bright with burning desire. He reaches for your hand and brings it to his mouth, pressing a deep kiss against your knuckles. "I want _you_." 

A surge of love and emotion rocks you and you smile so widely it hurts your cheeks. You lean forward until your chest is barely brushing him, keeping your lips a hair's breadth away from his. "I'm yours," you breathe. 

You give yourself over entirely. You let the fire consume you, pounding out a rhythm of energy in your veins that moves your body on it's own, matching a pace set by Grillby under you. His hands are everywhere, clinging to you, leaving heated marks on your skin that only increase the heat burning you from the inside out. Murmured words of praise fall from him when his mouth isn't on you. He trembles, a force of energy focused utterly on you and in every touch, every thrust, you can feel the unbelievable power simmering below the surface. Knowing that you can keep up, that you can match him even on a level like this only spurs on your energy and your own desire to make him feel just as loved as he makes you feel. 

Your hands stay clasped together, a tether to each other that cannot be broken. Together, you chase that high, that edge of ultimate pleasure. When you reach it, you scream his name and utterly lose yourself in the feeling of melting before him until there are no barriers between you at all. He soon joins you, his free hand digging into your back as he comes undone, your name falling reverently from his mouth. 

When it's over, the two of you lay side by side, taking a few minutes to simply try and catch your breath. You're a little dizzy from the heat and intensity of the sex but holy crap, it was worth it. Grillby finally stirs, getting to his feet and moving to the kitchen to get you a bottle of water. You sit up as he returns, gratefully taking the bottle and chugging the whole thing down. He sits back down, letting his legs brush against yours. You set the empty bottle down and fold your arms on the tops of your knees, stretching your fingers out to encourage him to take them. He does so, intertwining his with yours. 

"So, have you changed your mind on the onesies?" you tease playfully. 

He rolls his eyes. "...Maybe it wasn't actually so bad," he admits. "I did enjoy taking it off." 

You snicker, squeezing his fingers. "I liked that part too." 

He leans over your knees, giving you a slow, deep kiss. "I love you," he murmurs. 

You smile against his lips. "I love you too." 


End file.
